Television picture analyzer



June 6, 1939. I U 2,161,643

TELEVISION PICTURE ANALYZER Filed April 21, 1937 Patented June 6, 1939.

PATENT. orrlce 2,161,643 TELEVISION PICTURE ANALYZER.

Heinrich Striibig, Teltow,

stadt Seehof, Germany,

near Berlin, Gartenassignor to the firm of Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application April 21, 1937, Serial No. 138,235 In Germany May 9, 1936 4 Claims. (01. 250- -166) This invention relates to a picture analyzer tube with a photo mosaic in which the picture currents are guided to a collecting electrode separate from the mosaic electrode.

Fig. 1 is a view in section of a picture analyzer tube embodying the features of my invention.

Fig. 2 is an enlarged view partly in section of a portion of the screen construction of Fig. 1.

Fig. 3 is a view in section of a modified electron multiplier for application to the analyzer tube of Fig. 1.

It is a known fact that the storage of the photocurrent flowing during the time of exposure is possible in such tubes so that the sensitivity is increased to 40,000 times more than that of analyzing tubes without storage at the number of scanning lines used at present. Nevertheless, very sensitive amplifiers are required for the transmission of these picture signals. Thereby, the sensitivity of such television transmitters is limited by the noise level of the amplifier. I

According to the invention, the sensitivity of the picture analyzer tube is increased by guiding the picture currents to a. collecting electrode 5 which is simultaneously the first electrode of an electron multiplier. It has been found that such electron multipliers have a considerably lower noise level than the conventional thermionic amplifiers. However, the focusing of the primary 3o electrons is required if these are derived from an electron source outside of the amplifier and are not generated inside of the electron multiplier, for instance, by photo activity. In a picture analyzing tube with a photo mosaic, howeventhe 5 focusing of the electrons liberated by the cathode ray beam from the mosaic electrode would lead to difiiculties as strong distortion of the field through which the cathode ray beam traverses would occur. The electron multiplier, which is to cooperate with the analyzer according to the invention, will therefore preferably be given such a shape that it allows a diffuse stream of incident electrons to be amplified.

As a rule the multiplier will be incorporated in the same vacuum space as the analyzer. The collecting electrode may then be given the shape, for instance, of a network 8. Other arrangements are also possible, for instance, to use a foil l9 as a collecting electrode, whereby different gas pressures may exist in the analyzing tube and. in the electron multiplier. The multiplier can be built up of electron-permeable electrodes 11.

Fig. 1 of the drawing shows an embodiment of 5 the invention. An electron gun H] of substantially any type known to the prior art, deflecting plates II and a mosaic electrode 2 are placed inside of the vacuum receptacle I. The mosaic electrode consists of the network indicated by 9 and a large number of isolated elements 93 which possess end surfaces l4 and 15. The latter form one conductor of individual condensers, whereas the other conductor, namely, the net 9, is common for all condensers. The device operates in such a manner that the light is incident from one side (left side in the drawing) whereas the scanning action by the cathode ray beam occurs on the other side. Accordingly, the left side is coated with a strongly photosensitive layer, whereas the right side is prepared to emit secondary electrons when impacted by the cathode ray beam. The tube is provided with a wall coating 3, 4, over the greater part of its length, which wall coating is interrupted at the point 5. Tht part 3 next to the cathode is held at anode potential, whereas the part 4 is held at a slightly lower potential. The photoelectrons liberated from the left side of the mosaic electrode 2 are drawn towards the electrode 6 which may be, for instance, at anode potential. erably near the mosaic electrode, the vacuum receptacle possesses a projection 1 in which the electron multiplier is disposed according to the invention. 8 indicates the first electrode to which the secondary electrons mosaic screen is scanned. The potential of this first electrode is chosen somewhat higher than that of the wall coating 4 so that all electrons are securely guided to the electron multiplier.

The described arrangement and the mentioned potentials represent only an example. It may be preferred to change the arrangement to that respect that several electron multipliers are arranged symmetrically to the mosaic electrode and connected in parallel. In this manner it is possible to obtain saturation of the electron current at a low accelerating voltage, and the field which is traversed by the cathode ray beam will then hardly experience any distortion. A further possibility is to form the electron multiplier as a ring surrounding the mosaic electrode.

As an electron multiplier, a system can be used in which the electrodes are held at constant potentials. An arrangement may also be used in which an oscillating discharge is maintained between two secondary emitting cathodes to which an alternating voltage is applied.

I claim:

1. A television picture analyzer comprising an evacuated envelope having therein an electron In one spot, prefare drawn when the gun, deflecting plates disposed about the undeflected ray axis of said gun'and adapted to be energized by deflecting potentials, a, screen disposed within said envelope opposite said gun, said screen comprising a conducting network having disposed therethrough and insulated therefrom a plurality of elements, said elementsbeing sensitized for secondary emission upon the side thereof directed toward said electron gun and being sensitized for photo-emission on the side thereof directed away from said electrongun, an annular collecting electrode disposed upon said envelope wall upon the side of said photoemissive elements away from said-gun,.a metallic conducting layer disposed inwardly upon the wall of said evacuated envelope between said secondarily emissive elements, and said: deflectin electrodes, a second wall coating disposed between said deflecting electrodes and said electronv gun, and a projection formed in said envelope between said secondarily emissive elements and said deflecting electrodes and having therein an electron. multiplying. device adapted to operate by the collectionv of diffused electrons.

2. A television picture analyzer comprising an evacuated envelope having therein a, photomosaic electrode for receiving an optical image thereon, an annular collecting electrode disposed Within. said envelope for collecting electrons emitted from said photo-mosaic electrode, and means for directing a cathode ray beam across the reverse side of said photo-mosaic electrode at velocities s'uflicient; to cause secondary electron emission, acollecting network disposed between said photo-mosaic electrode and said cathode ray source for collecting diffusely secondarily emitted electrons from said mosaic electrode, and an electron multiplier in the region of said secondary electron emission for receiving and amplifying diffuse electrons collected upon said net- Work.

3. A television picture analyzer as claimed in claim 1, wherein electron permeable electrodes constitute successive stages within said electron multiplier unit.

4'. A television picture analyzer as claimed in claim 1, wherein a collecting electrode for said electron multiplier comprises a metallic foil forming a gasetight seal between the portion of said envelope containing said photo-sensitive elements and said multiplying elements. H

- HEINRICH STRUBIG. 

